Process and composition for developing images and designs on metal



ZbZ'lUU United States Patent PROCESS AND COMPOSITION FOR DEVELOPINGIMAGES AND DESIGNS ON METAL John M. Cornish, Morris Plains, NJ.,assignor to Modern Engraving and Machine Company, Hillside, NJ acorporation of New Jersey No Drawing. Filed Aug. 15, 1958, Ser. No.755,122

Claims. (Cl. 41-43) My invention relates to a process for forming imagesand designs on metal surfaces.

The etching of metal surfaces is, generally speaking, a well-knowntechnique for forming a design on a metal surface. The method commonlyemployed is to cover a cleaned metal surface with a material which isimpervious, or at least substantially so, to the action of an etchingbath, remove portions of the material from those areas of the metalsurface which are to form the design, and thereafter to treat theexposed metal surface in an etching bath. The etching bath is commonlycomposed of an acidic material which has the facility of eating away atleast part of a metal surface by chemical action. Acids with thiscapability can be easily determined by reference to an electromotiveseries of various metals and tables of acid strengths, the chemicalaction primarily resulting in oxidation and dissolution of the metalwith release hydrogen. Other chemical reactions can also take place andoxidizing acids or other agents effect the process in an additionalmanner independent of the acid strength.

However, while it is thus known how to etch metal surfaces, it is stillimpossible to obtain all desired surface treatments or to predict thenature of a surface treatment which will be obtained from a giventreatment with etching baths containing different components and withdifferent metals.

The achievement of my invention lies in providing a novel process foretching metal surfaces which will provide a. particular desired surfacetreatment, namely a frosted background comparable to that formed byfinal embossing. This surface effect is one that is in great demand andan etching process to form it is highly desirable.

It is, therefore, an object of my invention to provide a processemploying particular types of etching materials which will achieve aparticular desired surface treatment yielding a frosted backgroundcomparable to an embossed background. A further object of my inventionis to provide a novel etching composition for use in such process.

The following description will fully describe my invention so that itwill be understood by those skilled in the art of etching. Thedescription will relate primarily to the technique of forming theprotective coating by a photographic or light sensitive process, but itwill be appreciated that this coating may be formed in otherconventional ways, although with disadvantages.

The sheet of metal, aluminum, on which the design is to be etched mustfirst be cleaned, and I prefer to do this with Tripoli powder. Thiscleaning is followed by treating the metal surface with pre-etchsolution of hydrochloric acid substantially saturated with salt. Aconcentration of hydrochloric acid of is best for this stage, butconcentrations within the range from 5% to may be used. After thistreatment, which may last from V2 to 3 minutes at normal temperatures,the plate is dried and then coated with a suitable light sensitivematerial. In this process if the temperature is below 65 F., thereaction is too slow to produce the desired matte QFFEPEt- E finish, butif above F., the reaction is too violent to control, is. no resist canbe made to hold in the metal. Many of these are known and commerciallyavailable and my invention is not limited to any particular suchcoating. After drying the coating, it becomes light sensitive andsubsequent operations must be conducted under nonactinic light.

The sensitized plate is exposed to the desired photo positive, in avacuum technique, with a suitable light source, such as a double carbonarc lamp of about 35 amperes. The plate is then developed with adeveloper suitable for the coating employed and dyed to make the imagevisible. It is now possible to work under normal illumination for therest of the process.

Flushing with cold water will remove the excess dye and the plate isthen dried. Any extraneous areas not to be etched may be staged out atthis point by applying a suitable coating material such as asphalt, andthe plate is then ready to be etched.

At this point, I employ a particular etching solution in order to obtainthe particular effect I desire, namely the desired frosted surface whichwill match that of final embossing. This solution contains ironperchloride to which has been added a quantity of salt-saturatedhydrochloric acid. The best iron perchloride solution will be at aconcentration of about 40 Baum and will contain, per gallon, about 12.8ounces of hydrochloric acid of about 31% concentration (the usualcommercial form) saturated with salt. The concentration of the ironperchloric solution may vary from 35 to 46, Baum, preferably 38 to 42,and the hydrochloric acid employed may vary from 5 to 20, preferably 10to 15, ounces per gallon of the perchloride solution. It is important touse the above-named ingredients for I have tested many other acids andfound them to be unsuitable. For instance, various combinations ofhydrochloric, hydrofluoric, and nitric acids have been tried; but onlythe above-described solution will give the effect I desire.

Shortly after the solution is applied, a violent etching reaction willset in and increase as the heat of reaction builds up. It is best tointermittently swab the surface with a suitable material such as cottonduring this period until the first sign of a white scale begins to floaton the surface. short period in the solution and is then removed andexposed to the air for a brief period, the pressure of oxygen in the aircausing the reaction to become very violent. The plate is then immersedin water to stop the etching process. Finally, the plate will be cleanedwith paint remover and steel wool to remove the protective coating.

The following example will further illustrate my invention:

Example A sheet of aluminum was cleaned with Tripoli powder and thentreated with a pre-etching solution of 10% hydrochloric acid saturatedwith sodium chloride, and dried. The plate was spray'coated with KodakPhoto Resist and dried under heat under non-actinic light. The coatedplate was then placed in a vacuum box and exposed under a photo-positiveto a double carbon arc lamp of 35 amueres at a distance of six feet forsix minutes.

The plate was developed in a solution of Kodak Photo Resist developerfor three minutes and dyed to make the image visible. After flushingwith cold water to remove excess dye, the plate was then etched.

The etching bath was prepared by adding 12.802. of concentratedhydrochloric acid saturated with sodium chloride to a gallon of 40 Baumsolution of iron perchloride. The plate was immersed in this bath at 70F. and after about 20 seconds a violent reaction set in. Every 30seconds the plate was swabbed with cotton until Emirate:

The etching is then allowed to continue for a l after about 120 secondsa white scale appeared on the surface of the bath. The plate was left inthe bath for an additional 45 seconds and then exposed to the air for 15seconds. The reaction was quite violent in this stage. The plate wasthen immersed in water and the etching stopped.

After cleaning the plate with paint remover, the final effect was foundto match the frosted background obtained from a final embossing.

It will be appreciated that the above example is not limitive of thescope of my invention as to the exact conditions employed therein. Thetime of treatment in the etching bath may be varied from 60 to 240seconds, preferably 120 to 190 seconds in actual operation and theexposure to air may be from 10 to 25 seconds, preferably from 12 to 20seconds. It will also be understood that, while I have described thepreparation of the etching bath by the convenient method of adding thehydrochloric acid solution to the iron perchloride solution, it is ofcourse the final composition of that solution which is important, andnot any manner of addition of the reagents thereof. Thus, ironperchloride solutions prepared by the common technique of adding a smallamount of hydrochloric acid to avoid hydrolysis are contemplated and maybe used.

The above description makes it clear that my invention has the verygreat advantage of avoiding the necessity of preparing and usingembossing rolls, tools, and dies to obtain an embossed effect.Preparation of embossing rolls, for instance, is an expensive anddifficult process and requires a technique such as that described inUnited States Patent No. 2,662,002. Especially in cases where only a fewplates are desired, the cost of making the embossing rolls, etc., can beprohibitive. My invention now enables such plates to be prepared, withthe embossed appearance, at a commercially practical cost.

While the invention has been illustrated in the specific examples, itwill be appreciated that it is limited only by the spirit and scope ofthe following claims.

I claim:

1. A process for forming etched designs on aluminum metal surfaces whichcomprises cleaning said metal surfaces, applying a pre-etch solution ofhydrochloric acid saturated with sodium chloride, drying thethus-treated metal surface, depositing an image-forming resist coatingon said metal surface, removing said coating from the area to be etched,and treating the thus coated metal surface with an etching solutionconsisting essentially of iron perchloride containing hydrochloric acidsaturated with sodium chloride.

2. A process of etching an image on an aluminum metal surface,pre-treated with a solution of hydrochloric acid substantially saturatedwith sodium chloride, which comprises, blocking out areas which are notto be etched and treating the remaining etching areas with a solutioncorresponding to a mixture obtained by adding from to 20 oz. ofconcentrated hydrochloric acid substantially saturated with sodiumchloride to a gallon of a 35 to 46 Baum of iron perchloride.

3. A process of etching an image on an aluminum metal surface,pre-treated with a solution of hydrochloric acid substantially saturatedwith sodium chloride, which comprises, blocking out areas which are notto be etched and treating the remaining etching areas with a solutioncorresponding to a mixture obtained by adding from to 15 oz. ofconcentrated hydrochloric acid substantially saturated with sodiumchloride to a gallon of a 38 to 42 Baum of iron perchloride.

4. An etching composition consisting essentially of an aqueous solutioncorresponding to that obtained by adding from 5 to oz. of concentratedhydrochloric acid saturated with sodium chloride to a gallon of solutionof iron perchloride having a concentration from to 46 Baum.

5. An etching composition consisting essentially of an aqueous solutioncorresponding to that obtained by adding from 10 to 15 oz. ofconcentrated hydrochloric acid saturated with sodium chloride to agallon of solution of iron perchloride having a concentration from 38 to42 Baum.

References Cited in the file of this patent UNITED STATES PATENTS2,211,400 Wood Aug. 13, 1940 2,270,712 Wood Jan. 20, 1942 2,283,170Batcheller May 19, 1942 2,336,846 Clark Dec. 14, 1943 2,762,694 NewmanSept. 11, 1956 FOREIGN PATENTS 484,159 Great Britain Apr. 28, 1938

1. A PROCESS FOR FORMING ETCHED DESIGNS ON ALUMINUM METAL SURFACES WHICHCOMPRISES CLEANING SAID METAL SURFACES, APPLYING A PRE-ETCH SOLUTION OFHYDROCHLORIC ACID SATURATED WITH SODIUM CHLORIDE, DRYING THETHUS-TREATED METAL SURFACE, DEPOSITING AN IMAGE-FORMING RESIST COATINGON SAID METAL SURFACE, REMOVING SAID COATING FROM THE AREA TO BE ETCHED,AND TREATING THE THUS COATED METAL SURFACE WITH AN ETCHING SOLUTIONCONSISTING ESSENTIALLY OF IRON PERCHLORIDE CONTAINING HYDROCHLORIC ACIDSATURATED WITH SODIUM CHLORIDE.